Field-induced quantum critical point in itinerant antiferromagnet Ti₃Cu₄

Magnetism exists on a spectrum spanning the local to itinerant limit. Theory in the local moment extreme is experimentally confirmed in magnetic insulators where the magnetism originates from unfilled electronic shells. However, in the itinerant limit, where magnetism stems from band effects, experiment lags theory as there are only three known purely itinerant magnets Sc₃In, ZrZn₂, and TiAu, raising the need for discovery of new such systems. Also, it is of interest to understand what happens as magnetic order is suppressed to T=0 via various tuning parameters towards a quantum critical point (QCP).

We present results on singles crystals of a new antiferromagnet with no magnetic constituent elements, Ti₃Cu₄. Electrical, thermodynamic and diffraction measurements reveal the itinerant nature of the magnetic order below 11.3 K, supported by DFT calculations. The magnetic order is suppressed towards a QCP with H_c=4.87 T. We provide evidence of a Fermi liquid to non-Fermi liquid behavior crossover convergent at the QCP, giving credence to a novel state near the QCP. This field-induced QCP in an itinerant system serves as an example of a QCP without the effect of Kondo correlations, and is essential to the unified theory of magnetism and global understanding of quantum criticality.